OK, I am not a history buff but at least wikipedia agrees that archduke was a title manufactured by a duke to make them look better.
The title was not used systematically until the 14th century, when the title "Archduke of Austria" was invented in the forged Privilegium Maius (1358–1359) by Duke Rudolf IV of Austria, called Rudolf the Founder (German: Rudolf der Gründer).
OK, I am not a history buff but at least wikipedia agrees that archduke was a title manufactured by a duke to make them look better.
So you maintain that the duke changed his title to archduke but that was not to make him look better. We may have to agree to differ on that point.